SEXUAL DEVELOPMENT OF THE TROPICAL SHORT-FINNED EEL, Anguilla bicolor bicolor OF THE SEGARA ANAKAN WATERS, CENTRAL JAWA, INDONESIA

A total of 289 specimens of tropical short-finned eel, Anguilla bicolor bicolor, was collected from the Waters of SegaraAnakan in May,September,October, and November 2004. Basic biological information including body weight (BW) and total length (TL), gonad morphology, gonad somatic index (GSI), and eye index (EI) among collecting specimen was examined in order to understand their sexual development. It was found that A. b. bicolorfrom Segara Anakan were greatly varied in body weight (10-900g) and total length (16-78cm), suggested their occured in different life stages (young eel and adult eel). Based on gonad morphology it was found that sexual development of the species could be separated into four groups, namely: female (17.6%), male (48.1%), intersex (32.2%), and undeveloped (2.1%). GSI were 0-3 in female, 1-9 in male, 0-4 in intersex, and 2-7 in undeveloped. EIwere 3-10 in female, 1-7 in male, 2-8 in intersex, and 1-4 in undeveloped. Positive relationship was found between EI and body weight and length of the species in each sexual development, but no correlation between GSI and body weight and length, except for female. Different from temperate eels that bigger in size but smaller in GSI and EI, tropical eel A. b. Bicolor was smaller in size but bigger in GSI and EI, suggested more earlier sexual maturation inthe tropic than in the temperate

Correspondence between otolith microstructual changes and early life history events in Anguilla marmorata leptocephali and glass eels

To determine the exact correspondence between otolith characteristics and early life history events such as metamorphosis, coastal migration and recruitment to estuaries, both otolith microstructure and microchemistry analyses were applied to a sequential developmental series of samples, e. g. leptocephali, a metamorphosing larva, oceanic glass eels, and coastal glass eels. Total length and age were 10.1-50.7 mm and 22-137 d in leptocephali, 46.3 mm and 147 d in a metamorphosing larva, 47.8, 48.6 mm and 159, 160 d in oceanic glass eels, and 47.9-54.8 mm and 119-168 d in coastal glass eels. Checks at hatching and first feeding were observed in all specimens, but metamorphosis and freshwater checks were observed only in some specimens. It was confirmed that the abrupt drop in otolith Sr : Ca ratios and drastic increases of otolith increment widths in the metamorphosing larval stage correspond to the onset of metamorphosis, and the decrease after the peaks suggested the completion of metamorphosis, because the metamorphosing larva had no decrease in incremental widths. The relatively conserved Sr : Ca ratios decreased sharply in synchrony with the increasing increment widths. This study provides the first direct evidence that these drastic changes in otolith microstructure and microchemistry actually occur during metamorphosis, which has been only hypothesized

Correspondence between otolith microstructual changes and early life history events in Anguilla marmorata leptocephali and glass eels

To determine the exact correspondence between otolith characteristics and early life history events such as metamorphosis, coastal migration and recruitment to estuaries, both otolith microstructure and microchemistry analyses were applied to a sequential developmental series of samples, e. g. leptocephali, a metamorphosing larva, oceanic glass eels, and coastal glass eels. Total length and age were 10.1-50.7 mm and 22-137 d in leptocephali, 46.3 mm and 147 d in a metamorphosing larva, 47.8, 48.6 mm and 159, 160 d in oceanic glass eels, and 47.9-54.8 mm and 119-168 d in coastal glass eels. Checks at hatching and first feeding were observed in all specimens, but metamorphosis and freshwater checks were observed only in some specimens. It was confirmed that the abrupt drop in otolith Sr : Ca ratios and drastic increases of otolith increment widths in the metamorphosing larval stage correspond to the onset of metamorphosis, and the decrease after the peaks suggested the completion of metamorphosis, because the metamorphosing larva had no decrease in incremental widths. The relatively conserved Sr : Ca ratios decreased sharply in synchrony with the increasing increment widths. This study provides the first direct evidence that these drastic changes in otolith microstructure and microchemistry actually occur during metamorphosis, which has been only hypothesized

Estimating the extended and hidden species diversity from environmental DNA in hyper-diverse regions

Species inventories are the building blocks of our assessment of biodiversity patterns and human impact. Yet, historical inventories based on visual observations are often incomplete, impairing subsequent analyses of ecological mechanisms, extinction risk and management success. Environmental DNA (eDNA) metabarcoding is an emerging tool that can provide wider biodiversity assessments than classical visual-based surveys. However, eDNA-based inventories remain limited by sampling effort and reference database incompleteness. In this study, we propose a new framework coupling eDNA surveys and sampling-theory methods to estimate species richness in under-sampled and hyper-diverse regions where some species remain absent from the checklist or undetected by visual surveys. We applied this framework to the coastal fish diversity in the heart of the coral triangle, the richest marine biodiversity hotspot worldwide. Combining data from 279 underwater visual censuses, 92 eDNA samples and an extensive custom genetic reference database, we show that eDNA metabarcoding recorded 196 putative species not detected by underwater visual census including 37 species absent from the regional checklist. We provide an updated checklist of marine fishes in the ‘Raja Ampat Bird's Head Peninsula' ecoregion with 2534 species including 1761 confirmed and 773 highly probable presences. The Chao lower-bound diversity estimator, based on the incidence of rare species, shows that the region potentially hosts an additional 123 fish species, including pelagic, cryptobenthic and vulnerable species. The extended and hidden biodiversity along with their asymptotic estimates highlight the ability of eDNA to expand regional inventories and species distributions to better guide conservation strategies

Cross-ocean patterns and processes in fish biodiversity on coral reefs through the lens of eDNA metabarcoding

Increasing speed and magnitude of global change threaten the world's biodiversity and particularly coral reef fishes. A better understanding of large-scale patterns and processes on coral reefs is essential to prevent fish biodiversity decline but it requires new monitoring approaches. Here, we use environmental DNA metabarcoding to reconstruct well-known patterns of fish biodiversity on coral reefs and uncover hidden patterns on these highly diverse and threatened ecosystems. We analysed 226 environmental DNA (eDNA) seawater samples from 100 stations in five tropical regions (Caribbean, Central and Southwest Pacific, Coral Triangle and Western Indian Ocean) and compared those to 2047 underwater visual censuses from the Reef Life Survey in 1224 stations. Environmental DNA reveals a higher (16%) fish biodiversity, with 2650 taxa, and 25% more families than underwater visual surveys. By identifying more pelagic, reef-associated and crypto-benthic species, eDNA offers a fresh view on assembly rules across spatial scales. Nevertheless, the reef life survey identified more species than eDNA in 47 shared families, which can be due to incomplete sequence assignment, possibly combined with incomplete detection in the environment, for some species. Combining eDNA metabarcoding and extensive visual census offers novel insights on the spatial organization of the richest marine ecosystems

Discrimination and Distribution of Two Tropical Short-Finned Eels (Anguilla bicolor bicolor and Anguilla bicolor pacifica) in the Indonesian Waters

A total of 272 glass eel specimens of the two tropical short-finned eels (Anguilla bicolor bicolor and Anguilla bicolor pacifica) were collected around Indonesian waters from 2004 to 2007. Field sampling was conducted in 11 estuaries (Krueng Aceh, Air Kertaun, Cibaliung, Citanduy, Pacitan, Palu, Dumoga, Poigar, Bone Bolango, Akelamo, and Pami River) that spread out from western to eastern Indonesian archipelagos. Objectives of the study were to understand subspecies discrimination and distribution as well as population study of the tropical short-finned eel species (Anguilla bicolor) in the Indonesian waters based on morphological analyses of body measurements and vertebrae counts. Although morphological key characters of ano-dorsal length as a percentage of total length (-2.13 ~ 3.92) and number of ano-dorsal vertebrae (-3 ~ 4) overlap between subspecies, specimens were assigned to one of two subspecies based on their reported range of distribution from the western Sumatera Island to the southern Jawa Island (A. bicolor bicolor) and from the western Sulawesi Island to the western Papua Island (A. bicolor pacifica). Cluster analyses based on Euclidean distance separated the tropical short-finned eel species into two major clades. The first clade consisted of subscpecies of A. bicolor bicolor from Cibaliung, Air Kertaun, and Pacitan River estuaries. The second clade consisted of subspecies of A. bicolor pacifica from Palu, Dumoga, Poigar, Bone Bolango, and Akelamo River estuaries. Interestingly, A. bicolor bicolor from Citanduy River estuary (Jawa Island) nested in the second clade. The results suggested that a single tropical short-finned eel species, A. bicolor, inhabit in the Indonesian Waters. However the species was ecologically and biologically separated into two clade of subspecies, i.e. a Western Indonesian Clade of A. bicolor bicolor derived from Indian Ocean and an Eastern Indonesian Clade of A. bicolor pacifica derived from Pacific Ocean

RECRUITMENT PATTERN OF JUVENILE FISHES INTO PAMI RIVER ESTUARY (WEST PAPUA, INDONESIA

Recruitment pattern of juvenile fishes into Pami River estuary, West Papua, Indonesia (S 00.80970, E.134.06050), was studied from July to October 2005. The study purposes were 1) to observe fish diversity in family level, 2) to observe fish abundance of each family, 3) to observe recruitment pattern related to abundance and tidal rhythm. Samples were collected using line transect method and identification procedure were done based on morphological characteristics. A total of 19 Families were identified, namely Acanthuridae, Ambassidae, Anguillidae, Apogonidae, Carangidae, Chlopsidae, Clupeidae, Congeridae, Elopidae, Engraulidae, Gerreidae, Gobiidae, Mugillidae, Platycephalidae, Callyonimidae, Siganidae, Syngnathidae, Terapontidae, Tetraodontidae. Fishes composition varied each month.  Family of Gobiidae was the most dominant juvenile fishes recruiting during this study with 32%, 69.5%, 84.3%, 71.3%, respectively. Other 8 families (Ambassidae, Engraulidae, Elopidae, Chlopsidae , Siganidae, Syngnathidae,  Congeridae , and Callyonimidae) had the lowest composition varied from 0.4% to 3.2%. Three different patterns in abundance during the recruitment time of juvenile fishes, 1) early night (18.00-21.00) was represented by Ambassidae, Chlopsidae, Clupeidae, Gerreidae, Terapontidae, 2) mid-night (22.00-01.00) was represented by Callyonimidae, Congeridae, Engraulidae, Mugilidae, Platycephalidae, Tetraodontidae, and 3) late night (02.00-05.00) represented by Acanthuridae, Apogonidae, Carangidae, Elopidae, Gobiidae, Siganidae, Syngnathidae. However, the peak of abundance occurred at late night (>50 specimens caught), and recruitment pattern of all juvenile fishes has been associated with tidal rhythm

BIODIVERSITY, DISTRIBUTION, AND ABUNDANCE OF THE TROPICAL ANGUILLID EELS IN THE INDONESIAN WATERS

In order to understand biodiversity, distribution, and abundance among the tropical anguillid eels in the Indonesian waters, inshore migration mechanism of the juvenile anguillid eel (glass eel) to the estuaries of western, central, and eastern region of Indonesian waters were examined using both morphology and genetic analyses. A total of 9 species/sub species of anguillid eels (Anguilla bicolor bicolor, A. nebulosa nebulosa, A. bicolor pacifica, A. interioris, A. borneensis, A. celebesensis, A. marinorata, A. obscura and A. megastoma) were recognized to recruit at the mouth of 15 rivers through Indonesian archipelago. Species/subspecies diversity and distribution of recruiting juveniles differs in the estuaries of each region. In the western region that represented by estuary of Krueng Aceh, Batang Antokan, Air Kertaun, Cibaliung, Citanduy, Progo, and Pacitan Rivers, three species and sub species (A. bicolor bicolor, A. nebulosa nebulosa and A. bicolor pacifica) were found. In the central region that represented by estuary of Mahakam, Palu, Dumoga, Poigar, Bone, and Poso Rivers, five species and sub species (A. borneensis, A. celebesensis, A. marinorata, A. bicolor pacilica and A. interioris) were found. In the eastern region that represented by estuary of Akelamo and Pami Rivers, four species (A. marinorata, A. interioris, A. obscura and A. megastoma) were found. During the 6 months investigation from May to October 2005, abundance of the juveniles was higher in the central region compared with western and eastern regions. These results were suggested that inshore migration mechanism of tropical anguillid eels recruiting in tropical estuaries of Indonesian waters differs among regions

Correspondence between otolith microstructual changes and early life history events in Anguilla marmorata leptocephali and glass eels

To determine the exact correspondence between otolith characteristics and early life history events such as metamorphosis, coastal migration and recruitment to estuaries, both otolith microstructure and microchemistry analyses were applied to a sequential developmental series of samples, e. g. leptocephali, a metamorphosing larva, oceanic glass eels, and coastal glass eels. Total length and age were 10.1-50.7 mm and 22-137 d in leptocephali, 46.3 mm and 147 d in a metamorphosing larva, 47.8, 48.6 mm and 159, 160 d in oceanic glass eels, and 47.9-54.8 mm and 119-168 d in coastal glass eels. Checks at hatching and first feeding were observed in all specimens, but metamorphosis and freshwater checks were observed only in some specimens. It was confirmed that the abrupt drop in otolith Sr : Ca ratios and drastic increases of otolith increment widths in the metamorphosing larval stage correspond to the onset of metamorphosis, and the decrease after the peaks suggested the completion of metamorphosis, because the metamorphosing larva had no decrease in incremental widths. The relatively conserved Sr : Ca ratios decreased sharply in synchrony with the increasing increment widths. This study provides the first direct evidence that these drastic changes in otolith microstructure and microchemistry actually occur during metamorphosis, which has been only hypothesized